The present invention relates to pre-amplifier circuits. More particularly, the present invention relates to a programmable read/write pre-amplifier circuit used in a data storage system having at least one magnetic disc.
Magnetic disc drives have read/write heads which are used for both writing data to a magnetic disc and reading data from the magnetic disc. During a write operation, a write signal is provided to a selected read/write head from a write control circuit. The write signal represents data to be encoded onto the magnetic disc. More particularly, the read/write head receives encoded digital data from a "channel" chip. The transitions of the signal received from the channel chip cause the write current flowing within the read/write head to reverse direction which, in turn, induces a flux reversal in the magnetized material of the medium.
During a read operation, the read/write head senses flux reversals from the magnetic disc. The flux reversals are encoded onto the magnetic disc during the write operation. Based on the flux reversals, the read/write head provides a read signal to a read circuit. The read circuit amplifies the read signal and a channel circuit recovers the data. The channel circuit then provides the data to a magnetic disc controller for further processing.
In certain types of magnetic recording, digital information is recorded at different frequencies, depending upon the position of a concentric track of a disc. For example, employing a technique called "zone-bit recording", information on different tracks is recorded at different frequencies. By using different recording frequencies at the inner and outer disc tracks, the physical spacing between flux reversals can be nearly the same throughout the surface of the magnetic disc.
However, in the recovery of signals from such magnetic discs, it is necessary to employ read pre-amplifier circuits which are capable of receiving and detecting the frequency of the data encoded on the magnetic media. The frequency varies from track to track by as much as two times over the radius of the disc.
Conventional data storage/retrieval systems require individualized read/write pre-amplifier circuits which are fabricated to accommodate the particular recording and retrieval frequencies associated with a specific disc drive. The read/write pre-amplifier circuit (i.e."pre-amplifier chip") interacts with the host computer through a controller. Although the controller performs various tasks, only a small minority of the controller functions affect the read/write pre-amplifier circuit.
More particularly, there are three principal control signals which pass between the controller and the pre-amplifier circuit. The first control signal determines the mode (i.e. read or write) of the pre-amplifier circuit. In the read mode, the pre-amplifier acts as a high gain, low noise linear amplifier to boost the peak-to-peak read signal. In the write mode, the pre-amplifier receives encoded digital data from the channel chip for recording on the disc.
With the second control signal, the controller determines the "chip enable" status of the read/write pre-amplifier. In other words, when the chip enable function is low, the pre-amplifier can be in either read or write mode, as determined by the controller. However, if chip enable is high, the chip is placed in an "idle" state. In an idle state, the read/write pre-amplifier is neither reading nor writing. Ideally, the pre-amplifier chip should consume the least amount of power when in the idle state.
The third control signal delivered from the controller to the read/write pre-amplifier circuit is the head select signal. Each disc in the drive stack has a "head" adjacent the top and bottom surfaces. Thus, there are 2N heads per stack, where N is the number of discs in the stack, but only one head is active at a given time. A binary coded head select signal chooses which head is selected. In conventional disc drive systems, there may be one to five head select signals, depending upon how many heads the particular pre-amplifier circuit is designed to serve.
Conventional systems require each disc drive to be fabricated with off-chip circuitry, which usually consists of passive elements such as resistors, connected to the read/write pre-amplifier circuit. The off-chip circuitry allows the systems to accommodate specific data characteristics of a particular disc drive and specifically, to accommodate the particular head and a given zone. Pre-amplifier circuits which could adapt to any type of disc drive would be a valuable contribution to the art.